During the manufacturing of web material, the web material may be conveyed from one location to another to process the web. For example, a coating may be applied to the web material as it is conveyed. In addition, the manufacturing of the web material may include a winding operation. For example, the web material may be unwound from a core to apply a coating to the web material, and, after the coating is applied, the web material may be re-wound back onto the core. The operations of conveying and winding of a web material may occur several times during manufacturing.
Apparatus and methods are known for conveying web material. U.S. Pat. No. 4,933,716 (Imamura et al) teaches a film carrier used for printing an image onto a light sensitive material. Conveying rollers 22,24 are arranged to transport the film. The conveying rollers are provided with large diameter contact sections for contacting both edge regions of the film. U.S. Pat. No. 4,641,939 (Kitner) relates to an automatic film threading apparatus wherein a pinch roller 16 and a powered film spool 52 grip and pull the edges of a threading leader assembly 15 to convey the film. The pinch roller has an upper and lower concave shape with the edges of the roller having a flat circumferential surface. U.S. Pat. No. 4,150,886 (Merkel et al) discloses a motion picture projection system comprising a capstan and pinch roller designed to eliminate the creeping of the film from between the capstan and pinch roller. The capstan's frictional surfaces are inclined inwardly, while the pinch roller's end frictional surfaces are frusto-conical and inclined inwardly in the opposite directions.
Apparatus and methods for winding web material differ from the apparatus and methods for conveying web material. If the web material is not wound properly, defects such as pressure marks and scratches can result, making the web material unsuitable for finished product. To produce a good quality wound roll by winding, a uniform hardness is preferred. To achieve the desired hardness, a known method is to provide a rider roller or pressure roller which presses against the outer circumference of the roll being wound, thereby providing a constant hardness-controlling linear pressure. Referring to FIGS. 1a and 1b, a web 10 of material is being wound onto a core 12, forming a wound roll 14 of web material. A contact roller or pressure roller 16 is in contact with roll 14 across the width of web 10. A force F biases pressure roller 16 toward roll 14 such that a zone of contact or nip 18 is formed between pressure roller 16 and wound roll 14. Such a biasing force F may be accomplished by mounting pressure roller 16 on a pivotable mechanism or slider mechanism. In operation, web material 10 is held in tension T as it is transported about a portion of pressure roller 16 and through nip 18 onto core 12. As illustrated in FIG. 1a, pressure roller 16 is being driven by a motor 20 (as shown by arrow A) while core 12 is free to rotate; such a configuration is generally referred to as a surface winder. In contrast, in FIG. 1b core 12 is driven by motor 20 (as shown by arrow A) while pressure roller 16 is free to rotate. This configuration is generally referred to as pressure roller assisted center winding.
Air entrainment occurs when a layer of air moving with the web becomes wound into the roll, particularly during high speed winding. The pressure roller is intended to reduce the amount of air which is wound or entrained into the wound roll, thus the pressure roller contacts the web material across its entire width. If the amount of entrained air is substantial, a lap of wound web may not make contact with a previous lap, and the newly wound lap may shift or move relative to the previous lap causing abrasions in the web material.
While a pressure roller may assist in the reduction of entrained air, high contact stresses can occur as a result of a high contact force between the pressure roller and the wound roll. Stress risers, such as areas of increased web thickness and the presence of dirt or other particulate material, can also increase the contact stress. These high contact stresses can cause pressure marks in the web material, thereby adversely affecting the web material. In a particular situation wherein the web material is photosensitive, one side of the web material may be coated with carbon black particles, which reduce light reflections during exposure of the photosensitive web. High pressures from the pressure roller may cause the transfer of these carbon black particles onto the underlying lap of web wound onto the roll, causing what is referred to as low density spots which adversely affect the image of the photosensitive material. In addition, nonuniformities across the width of the web, such as material thickness and material property nonuniformity, cause contact stresses to be concentrated in particular locations across the web width. This non-uniformity of contact stresses unbalances the web tension forces during winding, causing lap-to-lap shifting and resulting in abrasions. Yet a further problem encountered during winding is lack of sidewall straightness. Air entrainment is a contributor to sidewall nonstraightness, as is web thickness nonuniformity and material property nonuniformity.
Pressure roller assisted center winding, described above, is unsuitable for high speed winding applications having a large build-up ratio. That is, where the ratio of the wound roll diameter to the core diameter is high. With such a center winding configuration, the torque applied to the core to drive the wound roll must be transmitted through the entire wound roll. This can cause the roll to cinch, resulting in abrasions to the web material. To avoid cinching, the wound roll hardness should be high. However, to achieve hard roll conditions, high stresses and their associated adverse effects, as described above, may occur.
U.S. Pat. No. 4,877,196 (Heymanns) relates to a rider roller for use in a web winding machine. The rider roller comprises grooves arranged in its surface to facilitate the transport of entrained air to avoid puckers and wrinkles. Such pressure rollers may be unsuitable for web material coated with photosensitive material, such as 35 mm consumer film or motion picture film. Photosensitive web material is sensitive to pressure marks, low density spots, and scratches which can occur by the riding of the pressure roller on the wound roll of photosensitive material. If located within the image area of the photosensitive material, pressure marks, low density spots, and scratches can cause the web material to be unsuitable for salable product.
U.S. Pat. No. 2,877,957 (Hyman) discloses a nondriven pressure roller in a pressure roller assisted center winding configuration. The pressure roller has a metal surface which is stepped in profile to guide webs of differing widths onto a winding roll. As previously described, this winding configuration is unsuitable for high speed applications wherein the build-up ratio is high since a torque is applied through the winding roll. Further, for surface winding, the metal surfaces of Hyman are unsuitable for high speed winding of photosensitive web material since the metal can cause high contact stresses and provides inadequate traction capability for winding.
U.S. Pat. No. 2,353,044 (Kriegsheim) relates to a film magazine wherein the film on a delivery roll is wound on a take-up spool after being exposed. An arrangement of rollers are positioned against the delivery roll and the take-up roll to prevent uncoiling and provide tight winding. This winding configuration may be suitable for slow, intermittent winding onto the take-up roll, however, such a configuration is not suitable for continuous, high speed winding, for example, at 100 feet per minute or greater. Further, the roller arrangement is unsuitable for surface winding applications where adequate traction must be developed to prevent the pressure roller from scratching the web material.
In many situations, rolls are started by first detaching the web material from the pressure roller and then winding, by hand, several laps onto the core. If the web material is photosensitive, this starting procedure is conducted in low or non-light conditions. Accordingly, a winding apparatus and method should be conducive to starting the winding of a new wound roll in non-light conditions to improve the efficiency of the winding operation.
Accordingly, there exists a need for an apparatus and method for winding web material onto a core wherein air entrainment is reduced, a good quality wound roll is produced, and defects, such as pressure marks and scratching, are not introduced to the roll. Such an apparatus and method should be appropriate for photosensitive web material, suitable for imperfect web material (i.e., non-flat web material, non-uniform thickness), applicable to high speed winding applications, and minimize the difficulty in starting a new wound roll.